Novel PV/Li-Ion Energy Storage System Based on Non-balancing Cell Management

A novel topology of an energy storage system composed of PV panels and lithium-ion batteries was presented. For the individual module of the proposed system, the energy coupling between the photovoltaic panel and lithium-ion cell is achieved with the designed control unit. Besides, with the structural coupling of the photovoltaic panel and lithium-ion cell of the PV/Li-ion module, the non-balancing cell management (NBCM) for the lithium-ion cell is realized. The proposed system was verified by simulation and experiments. It is shown that, in the proposed PV/Li-ion module, with the low-voltage floating charging criteria, the approximate MPPT (maximum power point tracking) control was accomplished with the charge-discharge of the lithium-ion cell. In comparison with the schottky diode connection, the operation efficiency of the PV/Li-ion module is increased by about 8% when there is a nearly direct connection between the lithium-ion cell and the 30 W PV panel with nearly no intervening electronics (just MOSFETs, metallic oxide semiconductor field effect transistor). The novel topology of the NBCM PV/Li-ion system can be applied both in stand-alone photovoltaic-battery systems and in grid-connected photovoltaic power plants.